Hub-bearing race interface

ABSTRACT

Bearing hubs are typically machined in a lathe. Strict tolerances must be observed because, if the bearing fits too tightly in the hub, it may “lock up” and will not turn. An approach to relax the strict tolerances associated with these bearing hubs is to cut threads or parallel grooves (circumferentially) in the surface in contact with the outer race of the bearing. These threads or the high points between the grooves will deform (crush) when the bearing race is pressed in. The strain, then, in the bearing race is lessened due to the plastic strain of the hub, reducing the chance the bearing will lock up.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to machining. More particularly the present invention relates to a method and apparatus for relaxing the machining tolerance of a hub made to receive a bearing's outer race.

[0003] 2. Background Art

[0004] A hub for receiving an outer race of a bearing would usually be machined in a lathe. Tolerances for such hubs are often strict because a bearing race that is strained too greatly may lock up, while a loose fit may result in a bearing working its way out of the hub. Thermal variations during operation can cause additional strain, as well. An additional difficulty is that bearing outer races have their own tolerances, as well.

[0005] To ameliorate these difficulties, hubs have been splined or knurled to provide for greater strain within the hub when exposed to the same stress. Splines (running axially in the hub) require additional tooling and setup to machine; and permit grease to squeeze out of the bearing region. Knurling has not proved to be completely satisfactory due to a lack of depth (the radial distance between the upset region and the indented region). This lack of depth results in insufficient “crush zone,” and consequently, less relaxation of machining tolerances than desired. Furthermore, knurling is a deforming of the metal rather than a cutting away of metal, making a knurling structure somewhat unpredictable if it is desired to deform it a second time.

[0006] There is, therefore, a need for a method and apparatus for machining hubs in a lathe to receive bearings in a manner that relaxes the tolerances required.

SUMMARY OF THE INVENTION

[0007] A purpose of this invention is to provide a method and apparatus for producing bearing hubs having relaxed machining tolerances. Another purpose is to limit the machining to a lathe to reduce the tooling required and eliminate the time involved in changing machines.

[0008] A bearing outer race is typically pressed into a hub. This is to stabilize the bearing, disallowing it from moving excessively. With the outer race pressed into the hub, there is less chance the outer race will turn with the bearing. However, there is a danger that a bearing outer race will fit too tightly in a hub. This may be due to a small hub or a large outer bearing race. Either way, the bearing may “lock up” due to the large strain caused to the outer race.

[0009] A method to reduce the strain to the bearing's outer race is to remove some material from the region of the hub that is in contact with the race. This may take the form of threads or circumferential grooves (threads with no pitch). The threaded or grooved region will strain to a greater extent than a smooth region under the same stress. Therefore, the hub will “give” or “crush” plastically, yielding to the outer race. The result is adequate press to hold the bearing's outer race firmly, yet not so much as to cause the bearing to lock up.

[0010] Both threads and grooves are best machined on the lathe on which the rest of the hub is machined. This eliminates the need to perform a setup on another machine for splining, etc.

[0011] The novel features which are believed to be characteristic of this invention, both as to its organization and method of operation together with further objectives and advantages thereto, will be better understood from the following description considered in connection with accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood however, that the drawings are for the purpose of illustration and description only and not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows an axial or end view of a bearing hub.

[0013]FIG. 2 shows a cross-sectional view of the bearing hub of FIG. 1, including threads at the hub/bearing race interface.

[0014]FIG. 3 shows a cross-sectional view similar to FIG. 2 of the bearing hub of FIG. 1, but showing a second embodiment including circumferential grooves at the hub/bearing race interface.

[0015]FIG. 4 shows a bearing hub and bearings similar to FIG. 1 with some of the hub cut away.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] To increase the strain caused by the stress of pressing a bearing's outer race into a hub, some of the surface in the area of the hub usually in contact with the outer race can be removed. Metal that is strained, then, is able to move (crush) into the areas where metal has been removed. The removal of material can be carried out in the form of threads (with a finite pitch) or parallel, circumferential grooves (threads with no pitch).

[0017] An axial view of a bearing hub 100 is shown in FIG. 1. A cross-sectional view of the hub 100 is shown in FIG. 2. A bearing's outer race is pressed into the hub 100 from the left side in FIG. 2. It is pressed in until it comes to bear against the stop 200. Commonly the hub surface in contact with the outer race is machined substantially smooth. With the present invention, material is cut from this region. The machining may be in the form of threads 210 as shown in FIG. 2. In FIG. 3, a view of a bearing hub like that of FIG. 2 is shown. In this figure, a second embodiment of the invention can be seen with parallel, circumferential grooves and annular circumferential ridges 300. The circumferential ridges can also be referred to as “regions between the grooves.”

[0018] For example, machining for a nominally 7.5″ diameter hub 100 calls for threads 210 or grooves 300 on the order of 20 per inch and 0.073″ deep.

[0019] In FIG. 4, a bearing hub 100 with two bearings 400-401 installed is shown. A portion of the hub 100 has been cut away to show the bearing-hub interface. No threads 210 or grooves 300 may be seen in the area of the hub 100 in contact with the bearing races 410-411. However, FIG. 4 does show the relationship between bearings and a hub 100.

[0020] The above embodiment is the preferred embodiment, but this invention is not limited thereto. Consequently, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 

We claim:
 1. A method for relaxing machining tolerances of a bearing hub, the method comprising machining threads into a hub surface in contact with a bearing outer race.
 2. A method for relaxing machining tolerances of a bearing hub, the method comprising machining circumferential grooves in a surface in contact with a bearing outer race.
 3. The method of claim 1 wherein the threads are made to deform as the bearing outer race is pressed into the hub.
 4. The method of claim 2 wherein regions between the parallel, circumferential grooves are made to deform as the bearing outer race is pressed into the hub.
 5. An apparatus for relaxing machining tolerances of a bearing hub, the apparatus comprising: (a) the bearing hub; and (b) threads machined into a surface of the hub in contact with a bearing outer race.
 6. An apparatus for relaxing machining tolerances of a bearing hub, the apparatus comprising: (a) the bearing hub; and (b) circumferential grooves machined into a surface of the hub and having circumferential ridges between adjacent grooves in contact with a bearing outer race.
 7. The apparatus of claim 5 wherein the threads are made to deform as the bearing outer race is pressed into the hub.
 8. The apparatus of claim 6 wherein the ridges between the parallel, circumferential grooves are made to deform as the bearing outer race is pressed into the hub.
 9. An apparatus comprising: (a) an annular bearing hub having threads disposed on an inner surface thereof; (b) an annular bearing disposed inside of the bearing hub; and (c) an annular outer race disposed between and in contact with the bearing and the threads of the annular bearing hub whereby the threads will serve as a crush zone and deform if the fit of the outer race between the bearing and the bearing hub is too tight.
 10. An apparatus comprising: (a) an annular bearing hub having annular ridges disposed between adjacent annular grooves on an inner surface thereof; (b) an annular bearing disposed inside of the bearing hub; and (c) an annular outer race disposed between and in contact with the bearing and at least some of the ridges of the annular bearing hub whereby the ridges and grooves will serve as a crush zone and deform if the fit of the outer race between the bearing and the bearing hub is too tight. 